There have been prevailed communication services that use communication IDs of terminals for authentication to ensure simplicity and security of the communication services. Each terminal retains addresses of the communication services in which the user participates and authentication information, such as the user IDs and the passwords, that enable the user to use the services. This allows the user to securely use a plurality of communication services. However, in the case where a terminal accesses a communication service via an access NW (network) different from the one that the terminal ordinarily uses to access the communication service, for example, in the case where the terminal accesses the communication service at a roaming location, a problem arises that the original communication ID cannot be used, and the user cannot use the service. Similarly, in the case where a sub ID, which is different from the original communication ID, is used to establish communication, the problem arises that the user cannot use the service.